Allowance for Loan Losses Rollforward by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Allowance for Loan Losses [Roll Forward]
Beginning balance	$ (10,552)	$ (9,016)	$ (14,203)	$ (19,084)
Benefit (provision) for loan losses	(466)	3,961	2,987
Write-offs	593	1,307	2,152
Recoveries	(94)	(75)	(240)
Other	153	(6)	(18)
Transition impact of the adoption of the CECL standard
Allowance for Loan Losses [Roll Forward]
Beginning balance		(1,722)
Single-Family [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	(9,344)	(8,759)	(13,969)	(18,849)
Benefit (provision) for loan losses	127	3,988	2,990
Write-offs	457	1,299	2,148
Recoveries	(93)	(71)	(240)
Other	153	(6)	(18)
Single-Family [Member] | Transition impact of the adoption of the CECL standard
Allowance for Loan Losses [Roll Forward]
Beginning balance		(1,229)
Multifamily [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	(1,208)	(257)	(234)	$ (235)
Benefit (provision) for loan losses	(593)	(27)	(3)
Write-offs	136	8	4
Recoveries	$ (1)	(4)	$ 0
Multifamily [Member] | Transition impact of the adoption of the CECL standard
Allowance for Loan Losses [Roll Forward]
Beginning balance		$ (493)